Halving the Barrier to Gas-Phase Oxidation of Bromide by Ozone

23 June 2025, Version 1
This content is an early or alternative research output and has not been peer-reviewed by Cambridge University Press at the time of posting.

Abstract

Recent atmospheric measurements have indicated that bromine and iodine may be responsible for up to 72% of halogen-induced ozone loss near the tropopause. Whilst the neutral bromine and iodine radicals have well-described reaction pathways with ozone, there is ongoing uncertainty regarding the multiphase chemistry of the corresponding bromide and iodide anions and thus the potential role of these ionic species in ozone depletion. Here, we demonstrate the unequivocal ozone-dependence of the archetype Br¯ + O3 reaction, which proceeds at ambient temperatures with an experimental rate constant of 8.9 (±4.4) × 10-15 cm3 molecule-1 s-1 (0.001% collision efficiency). Using a state-of-the-art computational approach, the reaction mechanism is revised to proceed via a singlet transition state with a calculated barrier of +22.1 kJ mol-1, substantially lower than prior estimates and not on the triplet surface as previously claimed. Statistical rate modelling using this new barrier height predicts a rate constant of 5.7 × 10-15 cm3 molecule-1 s-1 from canonical transition state theory, which is in excellent agreement with the experiment. This reconciliation of the kinetics for the intrinsic gas-phase reaction will enable systematic evaluation of temperature, pressure and solvation effects on this ion-molecule chemistry and thus inform the impact of both bromide and iodide anion chemistry on atmospheric ozone.

Keywords

Ozone
Bromide
Kinetics
Transition State
Kinetic Modeling

Supplementary materials

Title
Description
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Title
Supporting Information to Oxidation of Bromide by Ozone
Description
Additional details for mass spectrometry experiments and calculations. Further discussion on reaction pathways to generate molecular halogens. 79Br¯ + O3 experiments with increasing [ozone] and further discussion on the ion-trap kinetics. CCSD(T) energy diagram and discussion of the calculated structures along the reaction profile, along with details and results of the focal point analysis. Calculated barrier heights for the singlet TS using different active spaces and basis set sizes for both NEVPT2 and the hybrid CCSD(T)[NO] approaches, along with a sensitivity test for the latter. Justification for using canonical TS theory for kinetic model-ling. Cartesian coordinates and vibrational frequencies for all species calculated at M06-2X-D3/ma-def2-QZVPP (PDF).
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Comment number 2, Brad: Jun 23, 2025, 18:12

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Comment number 1, Brad: Jun 23, 2025, 18:12

Cybersecurity experts may ethically monitor social media and mobile devices in limited circumstances to protect individuals from threats, exploitation, or to aid criminal investigations, and to safeguard organizations by preventing data loss, ensuring regulatory compliance, responding to incidents, or combating malware. Monitoring can also enhance public safety through threat intelligence or fighting serious cybercrime. However, such actions are only ethical with strict safeguards, including explicit consent, transparency, proportionality in data collection, data minimization, secure storage, legal compliance, and robust oversight. Without these, monitoring risks becoming unethical and may infringe on privacy or legal boundaries. Guard Your Digital World With Innovative Tech! Do you require social media access, a phone hack, email breach or website security fix? OR Do you simply wish to recover lost crypto funds, detect/track a location or carry out data alterations? Our Elite cybersecurity services cover everything from result upgrades to clearing debts and fixing credit. For Unparalleled security and reliable results, choose the best in the business. For further assistance, contact cyberhelpdesk88@gmail.com or +1 862-660-2702 or Telegram: cyberhelpdesk00